This invention relates to medically implantable or insertable devices, and more particularly to devices which are designed to be detectable by ultrasound, and methods for enhancing ultrasound detection of these devices.
Medical science has devised a number of devices for long-term implantation or insertion into the human body. Some of these devices are prosthetic devices designed to replace natural parts of the body which malfunction. Common examples of such devices are false teeth, artifical hips, and synthetic blood vessels and heat valves. Other devices are implanted or inserted in the body to perform functions other than replacing existing natural parts. Common examples of such devices are pacemakers to regulate heart beat and intrauterine devices to prevent pregnancy.
Intrauterine devices are objects, foreign to the body, which are inserted inside the uterus to prevent pregnancy. The mechanisms through which they act are not completely understood by medical science. It is believed that intrauterine devices (IUDs) have been known since antiquity, finding their origin in the placement of stones in the uteri of camels to prevent pregnancies during long caravan journeys. Modern IUDs had their origin around the turn of the century with the introduction of the Richter silkworm gut IUD. During the 1920's and 30's, the Grafenberg ring and Ota ring were developed. Some examples of currently used IUDs include the Lippes Loop, the Saf-T-Coil, the Copper 7, the Copper T, and the Progestasert. The above-mentioned IUDs are of different shapes and different sizes. Generally, they are constructed of polyethylene or some other biocompatible plastic. The Copper 7 and the Copper T IUDs include a fine copper wire which enhances the contraceptive properties of the IUD. The Progestasert IUD includes progesterone which is selectively released into the uterus to both enhance the infertility-inducing properties of the IUD, and to reduce the undesirable complications caused by the IUD. Several IUDs are impregnated with barium or titanium dioxide to increase the radiopacity of the IUD, and thus make them visible on radiographs.
Most IUDs now include transcervical nylon tails, which monitor the correct placement of the IUD and facilitate its removal. Generally, the nylon tail extends partially into the vagina to enable the user to manually inspect for the presence of the IUD.
Several undesirable complications have been associated with the use of IUDs. Among these are infection, bleeding, uterine perforation, cervical laceration, septic abortion, ectopic pregnancy, and expulsion of the IUD by the user. Expulsion is undesirable in that if the IUD is expelled, it can no longer provide protection against pregnancy. For many of the above-mentioned complications, the examining physician must be able to detect the positioning and placement of the IUD in order to diagnose the problem, and to prevent further complications.
Perhaps the most common side effect of IUDs is abnormal bleeding, taking the form of either menorrhagia, metrorrhagia, or both. A disparity between the size and shape of the uterine cavity and the IUD and inaccurate (non-fundal) placement of the device at the time of insertion have both been linked to IUD-induced increases in uterine bleeding.
Another potentially very serious complication of IUDs is that of perforation. Uterine perforation is the penetration of the IUD through the wall of the uterine corpus. Cervical perforation is the penetraton of the IUD through the uterine cervix. Uterine perforations can be either complete or partial perforations. Complete perforations are those perforations wherein the IUD has completely passed through the uterine wall. Partial perforations are those wherein part of the IUD is still within the uterus or myometrium. Perforations can be either primary or secondary. Primary perforations are those perforations which occur at the time the IUD is inserted into the user. Secondary perforations are those which occur after the IUD has been inserted. It is important for the examining physician to be able to detect the presence and location of IUDs in the user. Extrauterine IUDs have been reported to have caused intestinal obstructions and bowel obstructions resulting in serious complications. Further, deaths have been reported from amniotic fluid embolism following spontaneous abortion in the second trimester in association with uterine perforation.
Currently, there are several techniques for determining the presence and position of IUDs in the uterus. One technique involves the use of X-rays. Many IUDs are treated with various materials to be radiopaque. There are serious difficulties, however, associated with the use of X-ray detection. X-rays are believed to be capable of inducing chromosomal abnormalities in the ova contained in the ovaries. Because of the close spatial relation between the uterus and the ovaries, it is generally wise to reduce the use of X-rays in this area whenever possible.
Another detection technique involves the use of sounds. Sounds are instruments which are introduced into the body to detect foreign matter. Physicians also will often examine the marker strings which are attached to the IUD to detect the presence and position of the IUD. Another technique is to manipulate the uterus under fluorscopic examination. In some cases, a second IUD has been inserted into the uterus to serve as an intra-uterine marker to detect relative placement of the lost IUD. Also, various ultrasound techniques have been used to locate the IUD in the uterus.